Centrifugal switch



March 10, 1942. F. J. JOHNS CENTRIFUGAL SWITCH Filed Feb. 16, 1940 2Sheets-Sheet l INVENTOR WITNESSES: 3

grands .Ifo/7775.

ATTORNEY March l0, 1942. F, 1 JOHNS 2,276,043

CENTRIFUGAL SWITCH Filed Feb. 16, 1940 2 Sheets-Sheet 2 WITNESSES:INVENTOR ATTORN EY Patented Mar. 10, 1942 UIUTED @STATES PATENT OFFICEWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation ot Pennsylvania Application February 16, 1940, Serial No.319,2.82l

(Gl. Zlio-SQ) 8 Claims.

The present invention relates to speed-responsive circuit-interruptingdevices,- and more particularly to ac'entrifugal switch which isespecially adapted flor usewith single-phase induction'mo'tors foreffecting `a desired change in the connectionsofl the motor whenitreaches a predetermined speed of rotation.'

Single-phase induction motors usually have a main or running primarywinding1 and an auX- iliary or starting` primary winding which isdisplaced 'from` the main "winding on the frame of the motor.V The twowindingsare connected to the line in parallel, anda phase displacementis produced `between 'the currents inv them, either by designing themwith' diiierent ratios of resistance to reactance, as in the split-phasemotor, or by connecting a capacitor in series with the auxiliarywinding', as in the capacitor motor. The effect of the displacement of'the tw'o windings on the frame and the phaseY displacement betweentheir currents is to set up a revolving field, so that the necessarystarting torque for the motor can be developed. After the motor hasreached a speed of from 70% to 80% of synchronous speed, the startingwinding'is disconnected from the line, or in some types of capacitormotors, a. different value of capacitance is connected in the auxiliarywinding circuit. This change in connections is made at a predeterminedspeed by some type of speed-responsive device, which is usually acentrifugal switch. Such a switch is usually designed to open itscontacts when the motor reaches the predetermined speed and toremainopen until the motor has. slowed down to approximately 20%'to 30%of synchronous speed.'

The object of the present invention is to provide a centrifugal switchwhich is especially adapted for use with single-phase motors, and whichis of very simple and inexpensive construction.

Another object of the invention is to provide a centrifugal switch whichis easily assembled and adjusted and which is very reliable and positivein its action.

A further object of the invention is to provide a centrifugal switchwhich has very high currentinterrupting capacity, and which is suitablefor use with single-phase induction motors of the higher ratings', suchas 1 to 3 horsepower.

Other objects and advantages of the invention will be apparent from thefollowing detailed description, taken in connection with theaccompanying drawings, in which:

Figure l is a partial longitudinal sectional vieW of a single-phasemotor, showing the switch of the r`present invention in assembledposition;

Fig. 2 isa perspective view showing the stationary member of the switch;

Fig'. 3 is la perspective view showing the assembled rotating member;

Fig. 4 is a perspective View showing the movable 'element of therotating member;

Fig. 5 is a perspective view showing the fixed element of the rotatingmember;

Fig.'6 is a perspective View oi a weight bar;

Fig. '7 is a perspective View showing the movable element of a' slightlymodified'form of rotating member; and

Fig". 8 is a perspective View oi an assembled rotating member using themovable element of Fig. 7.

The switch of the present invention consists essentially of a stationarymember, generally indicated at I, which is adapted to' be secured to theend Irbracket or other stationary part of a motor, and a 'rotatingmember, generally indicated at 2, which is' adapted to be fixed on theshaft of the motor. The preferred manner of mounting this device in amotor is shown in Fig. l, which is'a partial longitudinal section of asingle-phase motor of more or less conventional construction, having alaminated stator core 3 o'n which vthe windings 4 are placed, and whichis supported in a Asuitable frame 5. The rotor member is secured on ashaft 6 and has a laminated core I 'o'n which a suitable winding 8,indicated as a squirrel-cage winding, is placed. The shaft is supportedfor rotation in a bearing" 9 which is mounted in the end bracket I3. Thestationary member I of the switch is mounted on the inside of the endbracket Ill concentric with the shaft' and' may be secured to thebearing boss.v The rotatable member 2 is secured to the shaft in such aposition that it extends into the stationary member I when the motor isat rest, as shown in Fig. l,

The parts of the switch are shown more in detail in Figs. 2 to 6,inclusive. Fig. 2 shows the stationaryy member I which consists of agenerally cup-shaped body II, formed of insulating material, and havinga central bore I2 of large enough diameter to permit the shaft of themotor to pass through it with a reasonable clearance. Diametricallyopposite portionsV of the body member II are cut away, as indicated atI3. to provide openings extending a considerable distance into thebottom of the cup-shaped body. Two contact strips I4 of brass, or othersuitable material, are fastened to the bottom of the body II at eachside in such a position that their ends extend into the openings I3 andare spaced apart a small distance, as clearly shown in Fig. 2. ContactsI5 of silver, or any suitable contact alloy, are fastened on each of thecontact strips I4. A spring member I6 is placed in the body member I Ion each side and secured to it in any suitable manner, as by rivets Eachof these spring members I6 has secured to it a movable contact I8 whichis in a position to bridge the fixed contacts I5, but which is normallyheld away from them by the spring. These springs may be of any suitableshape, the shape shown in the drawings being illustrative only, but theyshould be so arranged that they will normally hold the contacts I8 outof engagement with the fixed contacts I5, but permit them to be movedinto engagement with the xed contacts by the application of pressure tothe springs by the rotatable member 2 in the manner to be describedhereinafter. As described above, the stationary member I is intended tobe secured to the motor bracket, or other fixed part of the motor, andfor this purpose holes I9 may be provided in the body portion II for thereception of mounting screws.

The rotating member 2 of the switch is shown assembled in Fig. 3, andconsists of a fixed element or support and a movable element or plunger2|, which is supported on the fixed element 20. The fixed element orsupport 20 is shown more in detail in Fig. 5. This element is preferablymade of sheet steel, or similar material, and has a central annular ange22 which is adapted to be secured to the shaft of the motor by a press tor in any other suitable manner. rI'he support 2i] is formed with a pairof upstanding ears 23 at each end, and each of these ears 23 has a slot24 cut in it. The slots 24 are preferably disposed at an acute angle tothe axis of the shaft, as clearly shown in Fig. 5.

The movable element or plunger 2| is shown in detail in Fig. 4. Thiselement is preferably molded of a suitable insulating material, and hasa circular base portion of a diameter slightly smaller than the insidediameter of the body portion II of the stationary member I. The plunger2| has a central bore 26 of slightly greater diameter than the shaft ofthe motor so as to permit the plunger to move freely axially of theshaft, and axially extending ears 2'I are formed on the plunger on eachside of the bore 26. Each of the ears 21 has a slot 28 formed in itwhich is perpendicular to the axis of the shaft. The ears 21 arepositioned so that they will t between the ears 23 of the support 20.

The rotatable member 2 is assembled, as shown in Fig` 3, with theplunger 2| fitting between the ears 23 of the support 20 and the twoelements are held together by means of weight bars 29. Two of these barsare used, one on each side of the shaft, and they extend through theslots 24 and 28 and are held in position therein by means of washers 30,which are pressed or otherwise secured on the ends of the bars. It willbe seen that the position and arrangement of the slots are such that thebars 29 are free to move outwardly away from the shaft under the inuenceof centrifugal force, and this movement is opposed by helical springs 3|which extend between the ends of the bars 29 at each side of the shaft.These springs are preferably fastened in grooves 32 formed in the endsof the bars, and the two springs should be matched to have approximatelythe same initial tension.

The operation of the switch is as follows: The switch is mounted in themotor in a position such as shown in Fig. 1, the stationary member Ibeing secured to a stationary part of the motor with the shaft 6extending through the bore I2. The rotating member 2 is placed on theshaft 6 with the support 29 secured to the shaft to rotate with it andthe plunger 2| extending into the body portion II of the stationarymember I, as shown in Fig. 1 which shows the parts of the switch intheir positions when the motor is at rest. In this position, the base 25of the plunger 2| extends into the stationary member I and bears againstthe springs I6, holding the movable contacts I 8v against the fixedcontacts I5 to maintain the switch in its closed position.

, When the motor is started, the rotating member the body I| of thestationary member I.

2 rotates with the shaft with the plunger 2| still bearing against thesprings I6. The centrifugal force acting on the weight bars 29 tends tomove them outwardly of the shaft, but this movement is restrained by thesprings 3| until the motor reaches a predetermined speed, at which timethe centrifugal force overcomes the restraining force of the springs,and the bars 29 move outwardly away from the shaft. As will be seen fromFig. 3, this outward movement of the bars is guided by the slots 24 sothat the bars move both radially and axially of the shaft, and sincethey also pass through the slots 28 of the plunger 2|, this outwardmovement of the bars draws the plunger 2| axially of the shaft in adirection away from the stationary member I. When the plunger 2| is thuswithdrawn from the stationary member I, the springs I6 move the movablecontacts I 3 away from the fixed contacts I5, thus opening the switchand effecting the desired change in the connections of the motor. Itwill be obvious that when the motor slows down, the reverse action willtake place. When the centrifugal force decreases to a predeterminedvalue, the springs 3| will pull the weight bars 29 inward toward theshaft to the position shown in Fig. 3, and this movement of the barswill move the plunger 2| axially into engagement with the springs I6 toagain close the contacts.

A somewhat modified form of rotating member is shown in Figs. 7 and 8.The movable element or plunger has a central bore 36 of large enoughdiameter to permit the plunger to move freely on the shaft and acircular base 31 of slightly less diameter than the inside diameter ofThe plunger 35 is supported on a fixed element or support 33 as shown inFig. 8. The support 38 is generally similar to the support 20 describedabove and has a central annular flange 39 adapted to be secured on ashaft by a press t, and ears 46 at each side of the flange 39. Thesupport 38 differs from the support 20 in that the slots 4I in the ears40 are perpendicular to the axis of the shaft and are positioned nearthe bottom of the ears. Weight bars 42 extend through the slots 4| ofthe support 33 at each side of the shaft. These weight bars may besimilar to the bars 29 and are free to move outwardly away from theshaft under the influence of centrifugal force. The plunger 35 isconnected to the support 33 by means of links 43 which are pivoted atone end on the weight bars 42 and at the other end on studs 44 securedin holes 45 in the plunger 35. Each link 43 has a lug 46 at itsmid-point and a helical spring 4'I is secured between the lugs 46 oneach side of the shaft. The two springs 4l are matched to'haveapproximately the same initialk tension.

The operation of this, embodiment of thelinvention will be apparent.When the motoris at rest, the springs 4l` hold thebars 42in the innerends of the slots 4|, as shown in Fig. 8, andthe plunger 35 extends intothe stationary member i to holdthe movable contacts I against; the fixedcontacts I5` as previously described. When the motor is started, thebars; 42 tend to` move outwardly under the influence of centrifugalforce but this` movement is restrained by the springsA 4'1, actingthrough the links 4*;3. When the motor reaches a predetermined speed,the centrifugal force overcomes the restraining force of the springsandthe bars 42 move outward away from the shaft. The links 43,` arepivoted on fixed pivots 44 on the plunger 35 and outward movement of thebars 42 therefore moves the plunger axially, withdrawing it from thestationary member I and permitting the contacts to open. When the motorslows down, the springs 4l pull the bars 42 inward when a predeterminedspeed is reached and thus move the plunger 35 axially into thestationary member to close the contacts. This type of rotating memberhas the advantage that by properly proportioning the linkage, it can bedesigned to open the contacts at a relatively high speed and to let themremain open until the motor has slowed down to a very low-speed.

It will be seen, therefore, that av centrifugal switch has been providedwhich is very reliable and positive in its action, and which is ofsimple and inexpensive construction. The stationary member requiresriveting, but is very simple in design and can be easily and quicklyproduced, while the rotating member requires no riveting or similaroperations, and can be very rapidly produced and assembled. The switchhas a very high current-interrupting capacity and will safely interruptcurrents as high as 120 amperes, making it suitable for use with thelargest sizes of single-phase motors and for similar heavydutyapplications.

It will be understood that various changes in design may be made withoutdeparting from the spirit of the invention. In the rotating member ofFigs. 3 to 5, the slots 24 of the support 20 may be shaped so as to givethe switch any desired type of operation. Thus, they may be shaped sothat after the switch has opened at a given speed, it will remain openuntil the motor has slowed down to a much lower speed, which is usuallydesirable. The slots mayalso readily be shaped so as to make the switchopen with a snap action, which is sometimes desirable. Similarly, thelinkage of the rotating member of Figs. '7 and 8 may be modified to makethe switch operate in any desired manner. The switch is easily adjustedto cause it to operate at the desired speed by initially adjusting thetension of the springs 3l or 41, which determines the speed at which theswitch will operate.

It is to be understood, therefore, that although certain specificembodiments of the invention have been shown for the purpose ofillustration, it is not limited to the exact structure shown anddescribed, but in its broadest aspects it includes all equivalentembodiments and modifications which come within the scope of theappended claims.

I claim as my invention:

l. A centrifugal switch comprising a stationary member having a pair ofcontacts thereon,

means on the stationary member for biasing the contactsto thev openpositiom a rotatable member including a fixed, element adapted to besecured on a shaft, for rotation therewith and a movable elementlsupported on thefixed element and movable axially of the shaft, saidmovable element being in engagement with the stationary memberwhen theshaft is at rest to hold the contacts closed, and a pair of Weight barsextending through slots in both the xed and movable elements, said slotsbeing arranged to permit the bars to move outwardly of the shaft underthe influence of centrifugal force and the slots in the xed elementbeing disposed to cause the movable element to be moved away from thestationary member by outward,V movement of the bars.

2. A centrifugal switch comprising a stationary member having a pair ofcontacts thereon, means on the stationary member for biasing thercontacts to the open position, a rotatable member including a xedelement adapted to be secured on a shaft for rotation therewith and amovable element supported on the fixed element and movable axially ofthe shaft, said movable element being in engagement with the stationarymember when the shaft is at rest to hold the contacts closed, a pair ofweight bars extending through slots in both the fixed and movableelements, said slots being arranged to permit the bars to move outwardlyof the shaft under the influence of centrifugal force and the slots` inthe fixed element being disposed to cause the movable element to bemoved awa7 from the stationaryy member by outward movement of the bars,and spring means opposing outward movement of the weight bars.

3. A centrifugal switch comprising a stationary member having a pair ofcontacts thereon, means on the stationary member for biasing thecontacts to the open position, a rotatable member including a i'lxedelement adapted to be secured on a shaft for rotation therewith and amovable element supported on the fixed element and movable axially ofthe shaft, said movable element being in engagement with the stationarymember when the shaft is at rest to hold the contacts closed, a pair ofweight bars supported in the fixed element and movable outwardly of theshaft under the iniiuence of centrifugal force, links connecting theweight bars to the movable element, said links being so arranged thatoutward movement of the weight bars causes the movable element to bemoved away from the stationary member, and spring means opposing outwardmovement of the weight bars.

4. A speed-responsive circuit-interrupting device comprising astationary member and a rotatable member, said stationary member havinga fixed Contact and a movable contact thereon, means on the stationarymember for biasing said contacts to the open position, said rotatablemember having a fixed element adapted to be secured on a shaft forrotation therewith and a movable element movable axially of the shaft,said movable element engaging the stationary member when the shaft is atrest to hold the contacts closed against the action of the biasingmeans, a pair of weight bars on the fixed element, said weight barsbeing disposed in slots in the fixed element and guided by said slotsfor movement outwardly of the shaft under the influence of centrifugalforce, and spring means opposing outward movement `of the weight bars,

said weight bars being connected to the movable element so that outwardmovement of the weight bars causes the movable element to move away fromthe stationary member.

5. A speed-responsive circuit-interrupting de vice comprising astationary member and a rotatable member, said stationary member havinga fixed contact and a movable Contact thereon, means on the stationarymember for biasing said contacts to the open position, said rotatablemember having a fixed element adapted to be secured on a shaft forrotation therewith and a movable element movable axially of the shaft,said movable element engaging the stationary member when the shaft is atrest to hold the contacts closed against the action of the biasingmeans, said fixed element having portions extending parallel to theshaft, said portions having slots therein, weight bars disposed in saidslots and guided thereby for movementboth radially and axially of theshaft under the influence of centrifugal force, and spring meansopposing radial outward movement of the Weight bars, said weight barsalso passing through slots in the movable element, said last-mentionedslots extending radially of the shaft, so that movement of the weightbars outwardly of the shaft moves the movable element axially away fromthe stationary member.

6. A speed-responsive circuit-interrupting device comprising astationary member and a rotatable member, said stationary member havinga fixed contact and a movable contact thereon, means on the stationarymember for biasing said contacts to the open position, said rotatablemember having a fixed element adapted to be secured on a shaft forrotation therewith and a movable element movable axially of the shaft,said movable element engaging the stationary member when the shaft is atrest to hold the contacts closed against the action of the biasingmeans, said xed element having portions extending parallel to the shaft,said portions hav ing slots therein, and weight bars disposed in saidslots and guided thereby for movement outwardly of the shaft under theinfluence of centrifugal force, spring means opposing outward movementof the weight bars, and links connecting the weight bars to the movableelement to cause it to move axially away from the stationary member whenthe weight bars move outwardly.

7. In a speed-responsive switch, a centrifugal device comprising a fixedelement adapted to be fixed on a shaft for rotation therewith, a movableelement carried by said fixed element and movable axially of the shaft,a pair of weights supported in the fixed element for movement radiallyoutward from the shaft under the iniiuence of centrifugal force when theshaft reaches a predetermined speed of rotation, said weights extendingthrough slots in the fixed element which guide the weights in theiroutward movement, and means connecting the weights to said movableelement to effect axial movement of the movable element when the Weightsmove radially.

8. In a speed-responsive switch, a centrifugal device comprising a fixedelement adapted to be fixed on a shaft for rotation therewith, a movableelement carried by said fixed element and movable axially of the shaft,a pair of weights supported in the fixed element for movement radiallyoutward from the shaft, spring means opposing outward movement of theweights, said weights extending through slots in the fixed element whichguide the weights in their outward movement, and means on the movableelement connecting it to the weights and adapted to effect axialmovement of the movable element when the weights move radially.

FRANCIS J. JGHNS.

